I think the air flap only has two positions: recirculate and outside air. To keep the flow from varying radically based on speed, it is positioned in a relatively neutral pressure area...IOW, speed does not ram the air though, it must be pulled by the fan. Now, you can adjust where and how much the air does flow at the dash level, and various flaps can direct it to either the windshield or the footwell, but those are not 'volume' controlled except via the fan speed.
Cars of old rarely had a/c, so ramming the air in was appreciated, especially in the summer, but those days are mostly over, at least in some markets as a/c is standard on many more cars these days than those of old, so they are designed differently. Drag falls into that equation, too. At speeds over 30mph, using the car's climate control is more efficient than opening the windows because the extra drag is more than offset by the efficiency of the climate control. An a/c evaporator needs a fairly consistent air flow over it so it doesn't either ice up or produce air that is not cool enough so it can dry the air out. That doesn't happen well if the airflow alters via speed.